Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$121.52	13.283%	$137.6615	$137.66	$137.65	$137.70
Purchase #2	$228.60	13.236%	$258.8575	$258.86	$258.85	$258.90
Purchase #3	$118.41	7.803%	$127.6495	$127.65	$127.65	$127.60
Purchase #4	$100.75	4.827%	$105.6132	$105.61	$105.60	$105.60
Purchase #5	$200.99	12.114%	$225.3379	$225.34	$225.35	$225.30
Purchase #6	$215.30	5.169%	$226.4289	$226.43	$226.45	$226.40
Purchase #7	$53.66	13.475%	$60.8907	$60.89	$60.90	$60.90
7 purchase totals =	$1,039.23		$1,142.4392	$1,142.44	$1,142.45	$1,142.40